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Nature and characteristics of sound waves - class-IX

Description: nature and characteristics of sound waves
Number of Questions: 51
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Tags: physics world of sounds waves oscillations and waves sound
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Which of the following statements is correct?

  1. Sound travels as waves

  2. Sound travels in straight lines

  3. Sound is a form of energy

  4. All of these


Correct Option: A
Explanation:

Sound travels as mechanical waves. A mechanical wave is a disturbance that moves and transports energy from one place to another through a medium. In sound, the disturbance is a vibrating object. And the medium can be any series of interconnected and interactive particles. This means that sound can travel through gases, liquids and solids.

Solution A: Sound travels as waves.

Sound waves in air cannot be polarised because they are 

  1. progressive

  2. stationary

  3. transverse

  4. longitudinal


Correct Option: D
Explanation:

It is a conceptual and memory based question.

A pure sine wave is called 

  1. chord.

  2. melody

  3. tone

  4. overtone


Correct Option: C
Explanation:

A pure sine wave with a certain frequency is called tone.
option "C" is correct.

A supersonic jet produces waves in air. The wave front is

  1. ellipsoidal

  2. conical

  3. spherical

  4. paraboloidal


Correct Option: B
Explanation:

These waves are also called as shock waves, which are of conical shape when, a supersonic air craft moves faster than sound.

Which factors determine the quality of the note ?

  1. Wavelength.

  2. Frequency

  3. Time period.

  4. Wave form.


Correct Option: D
Explanation:

Quality is used to describe the quality of the waveform as it appears to the listener. Therefore,  the quality of a note depends upon the waveform. 
Two notes of the same pitch and loudness, played from different instruments do not sound the same because the waveforms are different and therefore differ in quality or tone.

State whether given statement is True or False
Wave form is equivalent to quality 

  1. True

  2. False


Correct Option: B
Explanation:

Quality is used to describe the quality of the waveform as it appears to the listener. Therefore,  the quality of a note depends upon the waveform. 
Two notes of the same pitch and loudness, played from different instruments do not sound the same because the waveforms are different and therefore differ in quality or tone.
Hence, quality of the sound is affected due to the change in its waveform.

Shock waves are produced by objects

  1. carrying electric charges and vibrating

  2. vibrating with frequency greater than 20000Hz

  3. vibrating with very large amplitude

  4. moving with a speed greater than that of sound in the medium


Correct Option: D
Explanation:

Shocks are caused by objects moving faster than the speed of sound in the medium.
(The shock tries to bring the velocity of the fluid in the medium to subsonic).

Sound waves are not transmitted to long distance because,

  1. they are absorbed by the atmosphere

  2. they have constant frequency

  3. the height of antenna required, should be very high

  4. velocity of sound waves is very less


Correct Option: A
Explanation:

Sound waves are not transmitted to long distance because they are absorbed by the atmosphere. 

A sound is produced by plucking a string in a musical instrument, then

  1. the velocity of wave in the string in equal to the velocity of sound in the string.

  2. the frequency of the wave in the string in equal to the frequency of the sound produced.

  3. the wave in the string is progressive.

  4. the tension in string varies from point to point.


Correct Option: B
Explanation:

Frequency of the wave is the property which depends on source.

If A is the amplitude of vibration, then the time taken by a wave to cover a distance of 4A is known as

  1. Time period

  2. Half the time period

  3. 1 s

  4. 0.1 s


Correct Option: A
Explanation:

Time required to complete one vibration is T secs

In one full vibration, the particle covers a total distance of 4A

Thus, time required to cover a total distance of 4A during one vibration is T secs or 1 Time period

The correct option is (a)

A sound wave travels with a speed of 330 m s$^{-1}$ in air. If the wavelength of the wave is 110 cm, then frequency of the wave is _______.

  1. 100 Hz

  2. 200 Hz

  3. 300 Hz

  4. 400 Hz


Correct Option: C

Hertz is the unit of

  1. Wavelength

  2. Amplitude

  3. Frequency

  4. None of these


Correct Option: C
Explanation:

The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI). It is defined as one cycles per second.

If you go on increasing the stretching force on a wire a guitar, its frequency :

  1. Increases

  2. Decreases

  3. Remains unchanged

  4. None of the above


Correct Option: A
Explanation:

On increasing the stretching force on a wire in a guitar, the frequency also increases.

Loudness or intensity of sound depends upon:

  1. amplitude of soundwave

  2. area of vibrating body

  3. distance from the source of sound

  4. all of above


Correct Option: A
Explanation:

The intensity or loudness of sound depends upon  ,

(1) Amplitude (A) of vibration of the source ,
         $I\propto A^{2}$ ,
(2) Surface area  (a) of vibrating body ,
          $I\propto a$ ,
(3) Distance (r) of listener from the source ,
            $I\propto r$ ,  
(4) Frequency (f) of the source ,
            $I\propto f$ ,
(5) Density ($\rho$) of the medium  ,
          $I\propto \rho$ , 
(6) Motion of the medium , which changes the effective speed of sound .

The walls of the auditorium built for musical concerts should be such  that they are able to ______ sound. Fill in the banks.

  1. Transmit

  2. Refract

  3. Reflect

  4. Absorb


Correct Option: D
Explanation:

The walls of the auditorium should be equipped with good absorbing material , otherwise sound waves coming back after reflection from different walls may produce interference , constructive interference at any place in auditorium will produce a loud sound whereas distructive interference at any place in auditorium will produce a faint sound , making the music unpleasant . 

Which of the following parameters determines the loudness of sound ?

  1. Frequency

  2. Amplitude

  3. Wavelength

  4. Speed


Correct Option: B
Explanation:

When we change amplitude of vibration , volume of the sound also changes and due to volume of sound loudness will also change .

The _________ of sound depends on amplitude of vibration of the source.

  1. loudness

  2. pitch

  3. timbre

  4. frequency


Correct Option: A
Explanation:

The loudness of sound depends on amplitude of vibration of the source. Loudness of sound is directly proportional to the square of the amplitude of vibration producing the sound.

The more the amplitude of a vibrating body the more is the loudness. True or false.

  1. True

  2. False


Correct Option: A
Explanation:

The amplitude of a sound wave determines its loudness. Sound wave with a large amount of energy have a larger amplitude which increases the loudness in the wave. A large amplitude means a louder sound and a smaller amplitude means a softer sound.

Louder the sound less is the amplitude of vibrating body. State whether true or false.

  1. True

  2. False


Correct Option: B
Explanation:

Louder the sound more is the amplitude of vibrating body

Mark the incorrect statements.
(a) 
intensity of sound depends on the response of our ears
(b) 
loudness can be measured as a physical quantity
(c) 
loudness is a subjective quantity.

  1. a, b

  2. a, c

  3. b, c

  4. all of them


Correct Option: A
Explanation:

Intensity of sound is an objective quantity. It does not depend on the response of our ears. 
Loudness is a subjective quantity. It cannot be measured as a physical quantity.

A device based on multiple reflection used for sending amplified sound in a particular direction

  1. Bulb horn

  2. Megaphone

  3. Ear trumpet

  4. All


Correct Option: B
Explanation:

Megaphone is based on multiple reflection of sound. It is a horn shaped tube designed to send amplified sound in a particular direction. It is also called Loud hailer.

Mark the incorrect statement :

 a)intensity of sound depends on the response of our ears 

b)loudness can be measured as a physical quantity 

c)loudness is a subjective quantity. 

  1. a,b

  2. a,c

  3. b,c

  4. all


Correct Option: A
Explanation:

Intensity of sound is an objective quantity. It does not depend on the response of our ears. Loudness is a subjective quantity. It cannot be measured as a physical quantity.

How does Sound produced by humans?

  1. In humans sound is produced by the voice box

  2. In humans sound is produced by the larynx

  3. In humans sound is produced by the upper part of the wind pipe.

  4. all


Correct Option: D
Explanation:

In humans sound is produced by the vioce box or larynx. It is the upper part of the wind pipe. Two vocal cords are stretched across the voice box leaving a narrow slit. When the lungs force air through the slit, it vibrates and produces sound.

The greater the surface area of the vibrating body, the________is the loudness of sound.

  1. Lesser

  2. Greater

  3. Remains same

  4. None of these


Correct Option: A
Explanation:

Loudness of the sound  $L = 10 \log _{10} \dfrac{I}{I _o}$

where $I$ is the intensity of sound.
Greater the surface area of the vibrating body, lesser will be the amplitude of the sound and thus lesser will be the intensity of the sound.

Thus lesser will be the loudness of sound.

When we increase the loudness of sound of a TV, the property of sound that changes is:

  1. Amplitude

  2. Frequency

  3. Wavelength

  4. Speed


Correct Option: A
Explanation:

Loudness of sound is proportional to the intensity and amplitude of sound. So when we turn on the volume of tv, the amplitude of sound wave increases hence, loudness of sound increases 

So the answer is A.

Loudness of sound primarily depends upon

  1. Intensity

  2. Frequency

  3. Shape of the source

  4. Overtone


Correct Option: A
Explanation:

Loudness that we sense is related to the intensity of sound. 

The natural frequency of vibration of a system is called.

  1. Eigentone

  2. Eigenfunction

  3. Period

  4. Resonance


Correct Option: A

In order to reduce the loudness of a sound we have to:

  1. decrease its frequency of vibration of the sound

  2. increase its frequency of vibration of the sound

  3. decrease its amplitude of vibration of the sound

  4. increase its amplitude of vibration of the sound


Correct Option: C
Explanation:
Loudness of the sound  $L = 10 \log _{10}\dfrac{I}{I _o}$
where $I \propto A^2$   ($A$ is the amplitude of vibration of sound) 
Thus the loudness of sound varies directly as the square of the amplitude of vibration of the sound source.
Hence, the in order to reduce the loudness of sound, we have to decrease the amplitude of vibration of the sound.

A 1cm long vibrates with a fundamental frequency of 256Hz. If the length is reduced to 1/4cm keeping the tension unaltered, the new fundamental frequency will be

  1. 64

  2. 256

  3. 512

  4. 1024


Correct Option: D
Explanation:
We know that $n\alpha\cfrac{1}{l}$
Thus $\cfrac{n _2}{n _1}=\cfrac{l _1}{l _1}\\n _2=\cfrac{l _1}{l _2}(n _1)=\cfrac{1\times256}{(1/4)}=256\times4=1024Hz$

Two identical sound $A$ and $B$ each a point in the same phase. The resultant sound is $C$. The loudness of $C$ is $n$ $dB$ higher than the loudness of $A$

  1. $2$

  2. $3$

  3. $4$

  4. $6$


Correct Option: D

Arrange the following sounds in the increasing order of frequencies:

  1. roaring of a lion

  2. buzzing of a bee

  3. a baby's voice

  4. a woman's voice

  5. a man's voice


Correct Option: A

If the intensity of sound increases by a factor of $10^5$ , the increases in the intensity level is

  1. $5db$

  2. $10db$

  3. $25db$

  4. $50db$


Correct Option: A

In a class of $100$ students each shouting at $100 dB$. Find noise level of class

  1. $10 dB$

  2. $100 dB$

  3. $12 dB$

  4. $120 dB$


Correct Option: B

The fundamental frequency of a closed organ pipe is same as the first overtone frequency of an open pipe. The length of open pipe is $20\ cm$. The length of closed pipe is

  1. $25\ cm$

  2. $12.5\ cm$

  3. $13.33\ cm$

  4. $200\ cm$


Correct Option: C
Explanation:
Given $:- $
Fundamental Frequency for the Open orange pipe $= ν/2l'$
where$, ν =$ Frequency and l' is the length of the open orange pipe$.$
Third Harmonic of the orange pipe $= 3ν/4l$
where$, ν =$ frequency 
and $l$ is the length of the Closed orange pipe $= 20 cm.$
Now$,$ According to the Question$,$
$3ν/4l = ν/2l'$
$⇒ 3/(4 × 20) = 1/2l'$
$⇒ 3/80 = 1/2l'$
$⇒ 2l' = 80/3$
$⇒ l' = 40/3$
$⇒ l' = 13.33 cm.$
Hence,
option $(C)$ is correct answer.

Two loud speakers are being compared, and one other. The difference in intensity levels between the two when measured in decibels.

  1. 60

  2. 40

  3. 50

  4. 30


Correct Option: A

If the amplitude of a wave is doubled, what will be the effect on its loudness ?

  1. increase four times

  2. increase two times

  3. decrease four times

  4. decrease two times


Correct Option: A
Explanation:

Loudness depends on the square of the amplitude of the wave. 


That is, $loudness\propto { \left( amplitude \right)  }^{ 2 }$

Thus, when amplitude of the wave is doubled, the loudness becomes four times.

Which of the following factors change when a sound gets louder?

  1. intensity

  2. Speed of the sound wves

  3. frequency

  4. decibel level

  5. wavelength

  6. amplitude


Correct Option: A,D,F
Explanation:

When a sound gets louder , its amplitude increases , as intensity $I\propto A^{2}$ (amplitude) , therefore intensity of sound also increases , which in turn increases level of intensity i.e. decibel .

With the increase in frequency a sound becomes louder. True or false

  1. True

  2. False


Correct Option: B
Explanation:

Increased frequency means decreased wavelength and higher pitch/ sharpness. So increase in frequency makes sound more sharper while higher amplitude or higher intensity makes louder sound. 

The characteristic of sound which distinguishes a feeble sound from a loud sound of the same frequency is -

  1. loudness

  2. pitch

  3. music

  4. noise


Correct Option: A
Explanation:
Loudness is the characteristic of sound which distinguishes feeble voice from loud voice.

A vibrating tuning fork is first held in the hand and then its end is brought in contact with a table. Which of the following statement(s) is/are correct in respect of this situation?

  1. The sound is louder when the tuning fork is held in hand.

  2. The sound is louder when the tuning fork is in contact with table.

  3. The sound dies away sooner when tuning fork is brought in contact with the table.

  4. The sound remains for a longer duration when turning fork is held in hand.


Correct Option: B,C,D
Explanation:

when the tuning fork is held in hand there is only air in contact to the fork and sound waves force the air particles to vibrate but when the fork is in contact with the table the sound waves will travel in table as well as air which is in contact with table top. The sound dies sooner as the waves travel much faster in solids and liquids than in gases.

The difference of sound level between two point is $30$ decibel. The ratio of pressure amplitude between points is : 

  1. $10$

  2. $20$

  3. $30$

  4. $32$


Correct Option: D

The pitch of the sound produced by a stretched string gets higher as the tension .....................

  1. Increases

  2. decrease

  3. same

  4. none of these


Correct Option: A
Explanation:

Pitch depends on string length and string tension.

  1. If the string's mass per unit length remains constant, for longer string, high tension will produce high pitch.
  2. If the string's length remains constant, for heavier string, the higher the tension will generate higher pitch.

The pitch of sound increases if its frequency

  1. increases

  2. decreases

  3. remains same

  4. cant say


Correct Option: A
Explanation:

The pitch of sound increases if its frequency increases
Pitch describes how high or low a tone is and depends upon the rapidity with which a sounding body vibrates, i.e., upon the frequency of vibration. The higher the frequency of vibration, the higher the pitch.

Sound wave P has a greater amplitude and a larger wavelength in air than sound wave Q. How do the loudness and pitch of P compare with the loudness and pitch of Q?
How do the loudness and pitch of P compare with the loudness and pitch of Q?

  1. P is louder and higher in pitch than Q

  2. P is louder and lower in pitch than Q

  3. P is quieter and higher in pitch than Q

  4. P is quieter and lower in pitch than Q


Correct Option: B
Explanation:
We know that pitch $\propto$ frequency.
wavelength of P $>$  wavelength of Q
$\implies$ frequency of P $<$ frequency of Q
$\implies $ pitch of P $<$  pitch of Q
now ,
loudness $\propto $ amplitude
So, P has more loudness as compared to Q.

Which figure indicates low pitch?

  1. True

  2. False


Correct Option: B
Explanation:

In figure B , wavelength (distance between two successive compressions or rarefactions ) is large therefore frequency will be smaller i.e. pitch is low .

The sound produced by an object vibrating with a high frequency is called _____________ .

  1. shrill or high-pitched sound

  2. deep or low-pitched sound

  3. heavy sound

  4. musical sound


Correct Option: A
Explanation:

The frequency determines the shrillness or pitch of a sound. If the frequency of vibration is higher, we say that the sound is shrill and has a higher pitch. If the frequency of vibration is lower, then we say that the sound has low pitch.

With the increase in frequency of a vibrating body the sound becomes shrill. True or false.

  1. True

  2. False


Correct Option: A
Explanation:

As the frequency of vibration of an object increases, the pitch or shrillness of sound produced by it also increases.

The characteristic of sound which distinguishes between a sharp sound and a dull sound is called loudness. True or false.

  1. True

  2. False


Correct Option: B
Explanation:

The characteristic of sound which distinguishes between a sharp sound and dull sound is called pitch

The shrillness of a sound depends upon frequency.

  1. True

  2. False


Correct Option: A
Explanation:

 Pitch is the characteristic of a wave by which sound wave appears shrill or grave. It depends upon the frequency of the wave. 

so the answer  is A.

A shrill sound has a _______ pitch and a dull sound has a _______ pitch.

  1. High, low

  2. Low, high

  3. Low, low

  4. High, high


Correct Option: A
Explanation:

a shrill sound has a high pitch and a dull sound has a low pitch .

so the answer is A.

State whether true or false :

Shrill sound is a high-pitch sound and a soft sound is a low-pitch sound.

  1. True

  2. False


Correct Option: A
Explanation:

The vocal cords of women are thicker than men , therefore they produce a shrill sound , which we know has higher frequency or higher pitch , whereas men's voice is grave , means low frequency i.e. lower pitch .

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